The present invention relates to a tapping circuit for tapping fluid from a main fluid circuit which comprises:
a hydraulic motor having a preferred operating direction and having a casing which defines an internal space and in which a cylinder block is disposed; and
at least two main pipes suitable for being put in communication with the cylinder block of the motor and constituting respectively, in the preferred operating direction of said motor a feed main pipe and a discharge main pipe;
the tapping circuit comprising means for tapping fluid from the main circuit and means for removing the tapped fluid to a pressure-free reservoir via a removal pipe.
The tapping circuit is, in particular, a replenishing circuit which taps fluid from the main circuit for the purposes of cooling it, or a flushing circuit, which taps fluid so as to inject it into the casing of the motor to stabilize the temperature thereof. It can also be a circuit which performs replenishing and flushing in combination.
Replenishing circuits are known that use a first replenishing valve constituted by a selector whose first two ports are connected to respective ones of the two main pipes, and whose third port is connected to a removal pipe via a second replenishing valve constituted by a flow-rate regulator. The first valve includes a slide suitable for taking up three stable positions, namely a neutral position in which its three ports are not connected together, so that replenishing is not performed, and two replenishing positions, in which the first port or the second port is connected to the removal pipe. The slide is caused to go between the three positions by the pressure difference existing between the two main pipes. That prior art is shown in FIG. 1 (described below).
Document EP-A-0 896 150 shows a replenishing circuit suitable for flushing the casing of a hydraulic motor. That circuit includes two replenishing valves disposed on respective ones of the two main pipes of the main fluid circuit of the hydraulic motor. Each of those valves is controlled by the fluid pressure in the pipe with which it co-operates to go between a neutral position in which it does not tap any fluid and a flushing position in which it taps fluid from said pipe and injects it into the casing of the motor.
An object of the present invention is to provide a tapping circuit that is simplified compared with the above-mentioned prior art.
This object is achieved by the fact that the tapping circuit of the invention further comprises a single tapping and removal valve connected continuously via a tapping pipe to a single one of said main pipes, the valve also being connected to the removal pipe, and by the fact that the main pipe to which the tapping and removal valve is connected is the main pipe that constitutes the discharge pipe in the preferred operating direction of the motor.
Contrary to the teaching of the prior art, the invention thus proposes to connect the tapping and removal valve to only one of the two main pipes. In the invention, the pipe is chosen appropriately as being the pipe which, in the preferred operating direction of the motor, is the discharge pipe.
The motor is a reversible motor (its rotor can rotate in two opposite directions) which has a preferred operating direction.
For example, it may be a motor serving to drive a vehicle in translation, in which case the preferred operating direction corresponds to the vehicle moving forwards.
It may also be a motor whose preferred operating direction is related to an operating parameter that is intrinsic to the motor, such as its efficiency, which is better in one direction than in the other.
For example, it may be a motor having two operating cubing capacities, of the type described in Patent Applications FR-A-2 588 616 and FR-A-2 780 450. In such a motor, in low cubic capacity mode, the distribution pipes that do not contribute to providing drive torque are connected to the discharge in the preferred operating direction, and they are connected to the feed in the non-preferred direction, in which they present resistive torque.
In the tapping circuit of the invention, a single tapping and removal valve is sufficient, and it is only connected, via a first port, to the tapping pipe, and thus to the main pipe which serves as the discharge pipe in the preferred operating direction of the motor, and, via a second port, to the removal pipe.
The tapping and removal valve of the invention serves very advantageously to perform a replenishing function for the purpose of cooling the fluid when the main circuit is a closed circuit.
Advantageously, the removal pipe is connected continuously to the internal space of the hydraulic motor via an injection segment which is provided in a cover portion of said motor, and the replenishing circuit further comprises a pipe for connection to a pressure-free reservoir connected to the internal space of the motor via a leakage return orifice of said motor.
In this advantageous configuration, the tapping circuit flushes the casing of the motor. The fluid tapped via the tapping and removal valve is injected into the casing via the injection segment, while the fluid present in the casing of the motor is removed therefrom via the usual leakage return orifice. In a closed circuit, it is possible to combine replenishing and flushing by cooling the fluid before re-injecting it into the circuit.
When it serves to flush the motor, and regardless of whether replenishing is also associated with the flushing, the tapping and removal valve is advantageously contained in a cartridge suitable for being mounted on said cover portion by being connected to said injection segment.
Thus, with a standard xe2x80x9cmotor bodyxe2x80x9d, it is possible, merely by changing the cartridge in which the tapping and removal valve is mounted, to choose the flushing mode best suited to the use in question.
Advantageously, the tapping and removal valve has a communication passageway between the tapping pipe and the removal pipe, and it includes means for causing the cross-sectional area of said passageway to vary as a function of the pressure difference between the tapping pipe and the removal pipe.
When the tapping (replenishing and/or flushing) is active, the tapping pipe and the removal pipe are interconnected via this communication passageway. Its cross-sectional area is variable so that the flow rate of tapped fluid is adapted to suit the operating conditions of the motor. Insofar as, in the invention, a single tapping and removal valve is sufficient to perform the replenishing function and/or the flushing function, it is easy, for any given use, to choose the most suitable valve by the shape of its communication passageway, and by the way in which the cross-sectional area of said passageway varies.
In which case, advantageously, the tapping and removal valve comprises a flow-rate regulator having at least one inlet suitable for communicating with the tapping pipe, an outlet suitable for communicating with the removal pipe, a constriction interposed between said inlet and said outlet, and means for causing the cross-sectional area of the passageway between the inlet and the outlet to vary in relation with the head loss through said constriction.
This configuration, which is simple and effective, makes it possible to cause the flow rate of tapped fluid (used for replenishing and/or for flushing) to vary as a function of the pressure difference between the tapping pipe and the removal pipe.
In a first advantageous variant, the tapping and removal valve has means for opening the communication passageway only when the pressure difference between the tapping pipe and the removal pipe is at least equal to a threshold value.
When the pressure difference between the tapping pipe and the removal pipe is relatively small, and less than the threshold value, fluid is not tapped so as not to consume, for this auxiliary function, fluid that is then necessary in some other portion of the circuit, e.g. for releasing the parking brake of the motor, when starting up the motor.
In another advantageous variant, the tapping and removal valve has means for opening the communication passageway only when the pressure difference between the tapping pipe and the removal pipe is greater than a threshold value and when said pressure difference is less than a limit value.
In which case, fluid is not tapped for replenishing and/or flushing not only in the above-mentioned situation of low pressure (e.g. on starting up the motor), but also in a situation in which the pressure in the tapping pipe is high. It is thus possible to avoid tapping a flow rate which would cause a loss of power.
In addition, the temperature of the fluid increases when the flow rate is high. Therefore, said limit value is preferably chosen so that, as a function of the flowrate/pressure curve of the motor, it corresponds to a flow-rate value that is less than the flow rate for which the temperature of the fluid is considered to be too high for it to be possible for the fluid to serve to flush the casing of the motor. Thus, flushing is not performed when conditions are not satisfactory.
In addition, when the motor is used in its non-preferred direction of rotation only in short situations, such as for reversing, fluid is not tapped because the pressure in the tapping pipe which, in said non-preferred direction, is connected to the feed main pipe, is momentarily high.
Advantageously, the above-mentioned threshold value is about 15 bars, while the limit value is about 25 bars. For example, the communication passageway is such that, when the pressure difference between the tapping pipe and the removal pipe is greater than the threshold value and, optionally, less than the limit value, the tapped flow rate is 6 liters per minute (l/min). For example, this is applicable for a circuit in which the maximum pressure is about 400 bars, and the maximum flow rate is about 100 l/min.